Carburetor



March 19, 1957 E. OLSON 2,785,880

CARBURETOR Original Filed Aug. 9, 1949 zgvfl 44 5 IN V EN TOR.

EL'MER OLSON ATTORNEY K M EQ ent application is a division.

,which this particular application relates involves the con CARBURETORElmer ()lson, Rochester, N. Y., assignor to General Motors Corporation,Detroit, Mich, a corporation of Delaware Griginal application August 9,1949, Serial No. 109,347, new Patent No. 2,694,560, dated November 16,1954. Divided and this application July 21, 1954, erial No. 444,731

2 Claims. (Cl. 261-64) This invention relates to carburetors forinternal combustion engines, most particularly those for automotive use,and is directed specifically to an improvement in the pump mechanismprovided to supply additional fuel during acceleration to preventleaning of the mixture when the throttle is opened to increase speed.

It has been found that with highly volatile fuels such as are now incommon use, the carburetor will, at times, get hot enough in hotweather, after the engine is stopped, to vaporize fuel in the cylinderof the accelerator pump below the piston therein and the formation ofthis vapor is effective to force solid fuel out of the pumpdeliverypassage and into the mixture passage. This creates an undesirablesituation and the effectis very much like that produced by percolation"in the fuel supply passages. If it continues long enough, the fuel levelin the supply chamber might be considerably reduced, in fact, thechamber might be completely emptied. This wouldobviously make subsequentstarting difficult, as starting could not be accomplished until the fuelsupply chamber was re-filled. This could only be done by prolongedcranking of the engine, which is obviously objectionable for variousreasons.

It is accordingly the primary object of the present invention to providemeans for permitting the escape of fuel vapor from the bottom of theaccelerating pump cylinder when the engine is not in operation, so as toprevent the forcing of fuel from such cylinder into the mixture passage.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings where- ""ferred embodiment of the presentinvention is bwn.drawings:

:F igiire1 l1 is a vertical section through the carburetor :j andaccelerator pump;

' FighreQZ is a detail section showing the fuel delivery Figure 13 is adetail view showing the passage conheating, the pump cylinder with thefuel supply chamber.

.;The present invention is shown as embodied in a carburetor such asillustrated in application S. N. 109,347

",of Elmer; Olson, filed August 9, 1949, now Pat. No.

2 ,694 ;560-,l issued November 16, 1954, of which the pres- Since theinvention to struction, of the accelerator pump only, the structure ofthe carburetor, other than the pump mechanism, will be only brieflydescribed.

The carburetor, which is of down-draft type, comprises three separatecastings 2, 4 and 6, positioned one above the other. The casting 2,which constitutes the air inlet,'is supported on top of the casting 4 inwhich the fuel chamber and the mixing chamber are positioned, and thecasting 4- is supported on the casting 6 in which the throttle valvewhich controls the quantity of fuel mix- 2,785,880 Patented Mar. 19,1957 ture supplied to the engine is rotatably mounted. Suitable gasketsare positioned between the castings 2 and 4, 4 and 6. The air inletpassage is indicated at 8 and this communicates with the mixing chamber10 in casting 4, from which combustible mixture is delivered to theoutlet passage 12in casting 6.

The admission of air through the passage 8 is controlled by a manuallycontrolled but unbalanced choke valve 14, secured to a shaft which isrotatably mounted in the casting 2, and the quantity of combustiblemixture supplied to the engine is controlled by a throttle valve 16secured to shaft 18 rotatably mounted in casting 6.

The operating connections for the throttle and choke valves constituteno part of the present invention and can be of any suitableconstruction. However, some of the connections are shown in Fig. 1 andare, therefore, very briefly described hereinafter. The throttle isoperated by the arm 20 secured to one end of shaft 1-8 and connected byan operating connection (not shown) to the usual accelerator pedal. Thechoke valve is operated by an arm 22, through a manual connection (notshown) extending to an operating member on the instrument panel. The arm22 is movable on the choke valve shaft and the shaft is operated throughthe medium of a torsion spring 24 in the manner described in thepreviously mentioned parent application. The arm 22 has a cam surfaceformed thereon which engages a l'aterally'extending car 26 integral witha lever 28, pivotally mounted on a boss 30 and engaged by a torsionspring 32, which is a return spring. At the lower end of lever 28 thereis a projecting ear 34 which is engaged by an adjustable screw 36 on theoperating arm 20 to determine the normal idle position of the throttleand also is moved by car 34, when arm 22 is actuated to fully close thechoke, so as to open the throttle slightly to effect faster than normalidling when the choke is fully closed at low temperatures.

Fuel is supplied to a chamber 40 in the casting 4 through a conduit 42connecting with a passage 44 in casting 2. A passage 46 in a nipple 48connects passage 44 with chamber 40, and flow through the passage 46 iscontrolled by a valve 50 which rests on an arm 52 operated by the usualfloat (not shown), in the conventional manner to maintain a constantfuel level in chamber 40.

Fuel flows from the chamber 40 to mainand idling fuel inlets through ametering plug 54 to a vertical passage 56 which connects at its upperend witha horizontal passage 58 formed in a tubular part of the casting2 which extends across the mixture passage. Fuel flows from this passagethrough a restricted nozzle 62 which terminates in a small venturi tube64 discharging into a large venturi tube 66 formed by the Wall of themixing chamber.

The passage 58 extends all the way across the mixing chamber and at theleft end connects with a vertical passage 68 in the casting 4, whichleads to the idling fuel inlet (not shown). A plurality of openings 76admit air to the passage to form an emulsion of fuel and air therein.

The arrangement of fuel passages above-described is the same as thatshown in the above-mentioned parent application and since the specificarrangement of such passages forms no part of the present invention, nomore detailed description is necessary herein.

A pump is provided which is operated by a connection extending to thethrottle operating mechanism, and which supplies additional fuelwhenever the throttle is moved toward open position relatively rapidly,for the purpose of providing a mixture rich enough to bring aboutsatisfactory operation of the engine upon acceleration thereof.

Whenever the throttle is opened relatively rapidly, the increase in airflow is more rapid than the increase in fuel flow from the main nozzle62. This tends to lean the mixture, which would cause unsatisfactoryengine operation and the pump supplies additional fuel to offset thisleaning effect.

This pump includes a cylinder 72 formed in the casting 4 andcommunicating with a space 74 of generally cylindrical form in thecasting 2 and positioned immediately above the cylinder 72 when thedevice is assembled. A piston 76 is slidable in the cylinder 72 and issecured to a piston rod 78 which extends upwardly from the piston. Thepiston is operated by a connection operable by the throttle operatingarm 20 which includes a link 80 pivotally connected to the arm 20 and toa rod 82 slidable in a passage in the casting 4 and having a horizontalextension 84 at its upper end. This extension is received in a slot 86in the upper end of the piston rod 78 so that it can move relatively tosaid rod. The extension 84 engages a washer 90 which engages the upperend of a spring positioned between the washer and the top of piston 76.A spring 94 is positioned in the cylinder 72 between the piston and thebottom of the cylinder and normally holds the piston in its upperposition, as shown in the drawings.

Fuel is supplied to the space in cylinder 72 below the piston through apassage 96, connecting this space with the fuel chamber 40. A screen 98is positioned in the intake end of this passage and a check valve 100prevents fuel being forced out through such passage on the operativestroke of the pump piston. A fuel delivery passage also connects withthe cylinder 72 below the piston, this being the passage 102 in casting4, as shown in Fig. 2, which connects with passage 104 in the casing 2,that supplies fuel to a nozzle 106 which extends at an angle anddownwardly into the mixing chamber.

Adjacent its point of connection with passage 104 the passage 102 isenlarged as indicated at 108 to form a seat for a ball check valve 110,which is normally held seated by a spring 112, but which is forced offits seat upon the operative stroke of the pump piston. The spring 112 isreceived between the ball and a plug 114 which limits the upwardmovement of the ball and has a passage 116 to permit passage of fueltherethrough. The spring is of sufficient strength to hold the ballsealed under normal conditions, when the pump is not in operation, sothat no fuel will be normally drawn from the pump into the mixingchamber by the effect of suction on the delivery nozzle 106.

When the throttle is opened, the element 84 is moved downwardly. Thiswill normally compress the spring 92 to some extent before the pistonstarts to move downwardly. The piston will then continue to movedownward after movement of the throttle stops, so that normally, theaction of the pump is somewhat delayed and does not begin until thecompression of spring 92 is sufficient to cause the force exerted byspring to overcome the opposing force exerted by spring 94 and theresistance of the piston to movement. If the throttle is moved veryrapidly and far enough, the part 84 may be moved into engagement withthe bottom of slot 86 and the piston would be positively moved by itsoperating rod 82 during a part of its movement and would then movefurther as spring 92 expands after the throttle stops.

Since the bottom of the pump cylinder is quite close to the manifold, itis likely to get quite hot after the engine stops, particularly in hotweather, in fact, hot enough to vaporize the fuel standing in thecylinder below the piston. If there was no means for this vapor toescape, the pressure created thereby would force liquid fuel out throughthe pump delivery passage and nozzle 106 into the mixing chamber. Thebottom of the cylinder would then fill up again with fuel and theprocess described might be repeated for a considerable period of time,until the temperature dropped sufficiently for vaporization of fuel tocease. This action might be very objectionable and, indeed, might emptythe chamber 40 of fuel.

In order to prevent the occurrence described, means are provided topermit escape of fuel vapor from the space in the pump cylinder belowthe piston, so that no pressure will be created on the fuel therein,tending to force it into the mixing chamber. To this end, the piston 76has an axial passage 120 therethrough which connects with a passage 122in the piston rod 78 which leads to the space above the piston which isin registry with the space '74." and a vent tube 124 connects this spacewith the air intake. Any vapor escaping from the pump cylinder throughpassage 120 will eventually be discharged into the air inlet of thecarburetor.

The passage 120 is closed on the operative stroke of the pump piston bya ball check valve 126 which is moved upwardly to close the bottom ofpassage 120 by pressure of fuel on the ball, but normally when thepiston is not moving, the ball rests in the position shown in Fig. l, ontop of a short tube 128 and slightly spaced from the bottom of passage120 so that fuel vapor can escape through the passage between the balland the bottom of the piston, into passage 120 and eventually into theair inlet. The tube 128 is supported by four spaced ribs 130 connectingthe tube and piston and the end of the tube is so positioned withrespect to the piston that when the ball valve 126 is seated on top ofthe tube, as shown in Fig. 1, there is sufiicient space between the balland the bottom of the piston for any vapor which may form in thecylinder to pass between the ball and the piston and escape throughpassage 120. Obviously, as soon as the piston begins to move down on itsoperative stroke, the ball will seat against the end of passage 120 andprevent any fuel from passing through such passage.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In a carburetor having a mixture passage, a throttle controlling theflow of combustible mixture through said passage, a fuel supply chamber,means for supplying fuel to said passage, an accelerator pump actuatedby said throttle and operable to supply additional fuel on openingmovements of the throttle to enrich the mixture for acceleration, saidpump comprising a cylinder adapted to receive fuel from said fuel supplychamber and a piston slidable in said cylinder, means for preventing anyaccumulation of fuel vapor in said cylinder comprising a passageextending through the pump piston, said passage terminating in adownwardly opening conical portion, a valve coacting with said conicalportion to control flow through the passage, a cage carried by said pumppiston and comprising an elongated open-ended tubular member and aplurality of ribs supporting the tubular member in coaxially spacedrelation with the conical portion of said passage, said valve meansbeing normally seated upon said tubular member permitting fuel vapor topass around said ribs and through said passage, fluid in the tubularmember being adapted to move said valve means to seat within saidconical portion of said passage to prevent fluid flow therethroughduring the pumping stroke of said piston.

2. In a carburetor having a mixture passage, a throttle controlling theflow of combustible mixture through said passage, a fuel supply chamber,means for supplying fuel to said passage, an accelerator pump actuatedby"; said throttle and operable to supply additional fuel on openingmovements of the throttle to enrich the mixture for acceleration, saidpump comprising a cylinder adapted to receive fuel from said fuel supplychamber and a piston slidable in said cylinder, means for preventing anyaccumulation of fuel vapor in said cylinder comprising a passageextending through the pump piston, said passage terminating in adownwardly opening conical portion, a ball valve coacting with saidconical portion to control flow through the passage, a cage carried bysaid pump piston and comprising an elongated open-ended tubular memberand a plurality of ribs supporting the tubular member in coaxiallyspaced relation with the conical portion of said passage, a seat forsaid ball valve formed in the end of said tubular member adjacent saidconical portion, said ball valve normally positioned on said seatpermitting fuel vapor to pass around said ribs and through said passage,fluid in the tubular member UNITED STATES PATENTS 2,109,260 Chandler eta1 Feb. 22, 1938 2,212,946 Mock et al Aug. 27, 1940 2,493,804 CarlsonJan. 10, 1950

